There are several aims to this proposal. The first is to increase the understanding of irritable bowel syndrome, a prevalent, chronic stress-related disorder. Both psychological and physical factors are implicated in the presence and exacerbation of the symptoms. However, neither factor satisfactorily accounts for the symptom picture. Using a biopsychosocial approach, this study will examine the role of learning in the development and maintenance of symptoms. It is proposed that illness behavior may be learned through reinforcement of somatic complaints, operantly learning that being ill allows avoidance of undesirable events, and modeling. Stress is proposed to make the individual more susceptible to physical symptoms which makes reinforcement more likely. Twenty-five individuals diagnosed as suffering with irritable bowel syndrome will undergo a thorough multimodal assessment of illness history, operant learning experience, family environment, and psychophysio- logical stress response. Two comparison groups with 25 members each will be used; a second stress-related disorder, tension headache sufferers, and symptom-free controls. Support for a learning theory of illness behavior will be obtained if the two stress-related disorder groups do not significantly differ on the operant learning experience measures & psychophysiological stress response, and both significantly differ from the symptom-free controls If significant results are obtained, this has implications for future treatment studies. Awareness and modification of an individual's response to somatic symptoms (e.g., avoidance behavior) and the response of others (positive reinforcement) would be incorporated in a treatment strategy. The assessment strategies developed in this study can be used to monitor changes in these patterns (as a result of treatment). Furthermore, the effect of the treatment on members of the treated participant's family can also be assessed for potential "extra" benefits. Previous studies have found that children of irritable bowel syndrome sufferers are more likely to suffer from recurrent abdominal pain. If this somatic complaint is learned in part, then modifying parent's response is likely to benefit the child, even though the child is not a focus of treatment.